Written by J. Patrick Ford, DDS Friday, 07 March 2014 14:26
This is part 2 of a 2-part article series. Part one of Dr. Ford’s article was published in the January 2014 issue of Dentistry Today and can be found in our archived articles at the Web site dentistrytoday.com.
The stress axis/DNA protocol for dentures is a DNA-based denture technique that standardizes both chair-side and laboratory procedures, thus providing an economically produced, personalized, high-quality value denture to not only the modest and reduced-income financial demographic, but also may be integrated into premier and elite denture services.
Part one included the historical and scientific backgrounds and an overview of the clinical and laboratory basics of the stress axis/DNA denture protocol. This article, part 2 of this 2-part introduction, will demonstrate the stress axis/DNA denture protocol for an immediate denture case, for a case correction, and for a staged-treatment, 2-appliance case.
The following case histories are presented to demonstrate the efficacy of the stress axis/DNA denture protocol.
Case 1: The Immediate Denture
A 30-year-old patient with Down syndrome presented with a worn anterior occlusal architecture with no vertical-supporting posterior dentition distal to the premaxilla. The maxillary right cuspid and the mandibular left cuspid were the most posterior teeth in the dental arches. The preoperative models indicated an anterior, functionally rotated (Figures 1 and 2) premaxilla, causing maxilla-premaxilla diastemas (the upper left quadrant diastema is assumed). Due to the patient’s economic situation, no wax try-in appointment was scheduled.
After the DNA assessment and notching of the retromolar pads at the mandibular plane of occlusion, the case was mounted to the patient’s centric relation bite record on a semi-adjustable articulator (Dentatus USA). For articulator stability, the right and left condylar and Bennett articulator indices were set to zero degrees.
The increase in the vertical needed was set by placing the waxing template (Myotronics-Noromed) into the DNA-guided, notched retromolar pads and mounting the case to the vertical height of the mandibular left cuspid (Figure 3).
|Figure 1. Right lateral pre-op model.||Figure 2. Left lateral pre-op model.|
|Figure 3. Waxing template set to cuspid height.||Figure 4. Acrylic teeth set to cuspid height.|
Exposing the patient to iatrogenic temporomandibular disorders (TMD) was avoided by limiting the increase in vertical height to the existing height of the left mandibular cuspid. The balance of the dentition was set to the 8-inch, 17° DNA slope, waxing template (Myotronics-Noromed) (Figure 3).
To duplicate the incisal edge position, to reacquire the youthful incisal esthetics, and to maintain the emergence profile angle, each denture tooth used to replace the existing dentition was individually embedded into each cast (Figures 4 and 5).
The acrylic intaglio of the replaced maxillary and mandibular dentition was lab-adjusted prior to, and finalized at, the insertion appointment. In the stress axis/DNA denture protocol, the mandibular wax-up is completed prior to the maxillary wax-up. To compensate for the preoperative premaxillary rotation, the maxillary anterior teeth were distalized (Figure 5). The presurgical position of the maxillary right cuspid is also seen in Figure 5. To close the diastemas caused by the functional, anterior displacement of the premaxilla, a combination of Class I (right side) and Class II (left side) occlusal patterns was used. By utilizing a posterior Class II occlusal pattern, the patient’s left side premaxillary diastema was closed (Figure 6a).
|Figure 5. Original position of right maxillary cuspid.|
|Figure 6a. Left lateral—Class II.||Figure 6b. Right lateral—Class I.|
|Figure 7. Wax-up for anterior occlusion.|
|Figure 8. Full wax-up.||Figure 9. Left lateral.|
|Figure 10. Right lateral.||Figure 11. Frontal view at insertion.|
The right premaxilla-maxilla diastema reduction was accomplished by placing the maxillary right cuspid equidistant between the maxillary right lateral and maxillary right first bicuspid (Figures 6b to 8). The asymmetric reduction of the diastemas personalized the final esthetic result.
The deep vertical anterior occlusal pattern necessitated the use of the palatal acrylic (Diamond D Acrylic [Lincoln Dental]) for the anterior incisal occlusion (Figures 7 and 8). The acrylic was lab adjusted to provide only centric occlusal stops.
Again, the case instructions to the dental laboratory team did not include a wax try-in appointment. The clinician (familiar with the stress axis/DNA denture protocol) was kept informed during the laboratory process and made case decisions through digital images forwarded as standard jpeg e-mail attachments.
Excluding the surgical referral and post-insertion care, there were 2 appointments needed for this stress axis/DNA immediate denture case. The post-insertion images (Figures 9 to 11) indicate the normal results, which may be expected when using the stress axis/DNA denture protocol in similar immediate denture cases.
Having a known, stable, DNA-guided platform for the mandibular plane of occlusion permitted a high degree of certainty for the successful completion of this 2-appointment case. (Case history courtesy of John Murray, DDS, Glenwood Springs, Colo.)
Case 2: A Case Correction
The stress axis/DNA denture protocol provides not only a standard for the virgin or replacement denture case, but also a standard for a secondary evaluation, remounting, and finishing of an existing denture in progress.
After a requested stress axis/DNA denture re-evaluation of this full maxillary and mandibular denture wax try-in, the mandibular denture was determined to have been set into the freeway (speaking) space (Figures 12a and 12b).
The DNA-regulated mandibular plane of occlusion is the blue line below the waxed gingival margins of the mandibular right and left second molars (Figures 12a and 12b). When the mandibular model is set to the notched, DNA-corrected mandibular plane of occlusion (Figure 13), the mounting/waxing error is readily apparent.
The case was reset to the stress axis/DNA denture protocol, and after the approval of the wax try-in (Figure 14), the finished case (Figure 15) was inserted and remains trouble-free. (Case history courtesy of Charlie Belting, DDS, Alamosa, Colo.)
|Figure 12a. Line at left DNA-regulated mandibular plane of occlusion.||Figure 12b. Line at right DNA-regulated mandibular plane of occlusion.|
|Figure 13. Waxing template indicates waxing discrepancy.||Figure 14. DNA-regulated wax try-in.|
|Figure 15. Completed case.||Figure 16. Maxillary denture waxed to the DNA-regulated plane of occlusion.|
Case 3: Staged (Delayed) Treatment
This maxillary denture patient delayed the construct of a mandibular-opposing bilateral-free-end partial. A “dummy” partial was waxed to the DNA-guided, mandibular plane of occlusion, stress axis/DNA denture protocol (Figure 16). This assured the correct, DNA-regulated, mandibular plane of occlusion for any future mandibular removable or fixed appliance(s). (Case History courtesy of Michael Gadeken, DDS, Grand Junction, Colo.)
In January 2008, 20 million Americans qualified for food stamp assistance. Currently, more than 47 million persons in the United States have been enrolled in the food stamp assistance program. This is an increase of more than 27 million individuals in the last 5 years. Dental services will continue to be needed in all financial demographics, but these data suggest that expenditures for elective, nonemergency, dental services will be modified or postponed.
To address the changing economic demographics, both dental laboratories and dental offices can expect the stress axis/DNA protocols to provide a reliable, efficient, reproducible, evidence-based template for removable dental prosthetic procedures. Adding the retromolar pads to an impression and the midline maxillary and mandibular attached gingiva to lip-line heights to a laboratory prescription is not difficult. The 8-inch waxing templates with vertical posts, if not already in the laboratory’s inventory, are readily available (Myotronics-Noromed). Economical modifications to existing equipment may be necessary. An articulator with adjustable anterior guide pin is recommended.
The DNA and stress denture protocols are an outgrowth of a value denture service to the modest and reduced income demographic. These same principles may also be used for premier and elite denture services.
This introduction to the Bimler stress axis, the golden mean gauge, and the 8-inch (17° double-helical DNA slope) protocols is offered as a procedural complement to existing value, premier, and elite denture services.
IN CLOSING: A SYNOPSIS OF THE PROTOCOL
Stress axis/DNA full denture protocol involves the construction of a maxillary and mandibular full denture set based on 4 treatment data sets of information. These 4 treatment data sets are as follows:
- The first is mounting the mandibular edentulous cast to Bimler’s cephalometric factor 6, which is a bone-to-bone measurement of the stress axis of the mandible to the maxilla;
- The second is the determination of the posterior boundary of the freeway (speaking) space and the height of the mandibular plane of occlusion in the edentulous (or partially edentulous) mandible utilizing the overlapping DNA width/length proportion evidenced in the golden mean gauge (Dental Designs by Dentists);
- The third and fourth are setting the anterior speaking space determinants to the maxillary and mandibular midline lip heights (measured from the attached gingiva to the height of each lip).
Standard working casts that include complete bilateral impressions of the retromolar pads are poured and trimmed. The clinician-technician team outlines the retromolar pads and utilizes the golden mean gauge (Dental Designs by Dentists) to mark the overlapping length-to-width ratio of the DNA molecule, thus demarcating the posterior boundary of the freeway (speaking) space located between the maxillary and mandibular planes of occlusion.
The anterior boundary of the freeway (speaking) space is determined by the clinical dictates of the functional, speaking, and esthetic determinants. The maxillary and mandibular anterior midline lip heights, in both the relaxed and fully opened positions, are suggested anatomic referencing points to begin the location of anterior component of the freeway (speaking) space. In private clinical trials, the midline vestibular lip heights are very close approximations to the final placement of the anterior portion of the freeway (speaking) space developed through functional, speaking, and esthetic determinants. The third and fourth treatment/data sets—the clinical maxillary and mandibular midline vestibular lip heights—are noted on the laboratory prescription and then marked on the maxillary and mandibular occlusal (bite) rims.
Prior to mounting the mandibular edentulous cast to an articulator, the cast is notched at the caudal, DNA-determined, mark on each retromolar pad, the freeway (speaking) space being just coronal to these reference points. To orient both the posterior, DNA-determined, component of the mandibular occlusal plane height and the anterior, clinically determined, mandibular occlusal plane height (at the midline height of the mandibular lip), to the DNA-determined mandibular occlusal plane, the 8-inch, heated waxing template is placed into the DNA-determined and bilaterally notched retromolar pad fulcra and rotated into the mandibular wax bite rim, melting the bite rim wax to the height of these anterior and posterior determinants of the mandibular plane of occlusion. Because the 17° slope of the 8-inch waxing template corresponds to the 17° double-helical slope of the DNA molecule, the 8-inch waxing template is recommended for this procedure.
After the mandibular cast/base plate/wax bite rim complex is modified to the anterior and posterior determinants of the mandibular plane of occlusion, it is placed into the same waxing template used to heat-modify the wax bite rim. This mandibular (cast-baseplate-wax bite rim-waxing template) complex is mounted to an articulator as one unit. The full complement of mandibular teeth, selected in concert with clinician/patient preferences, are waxed and articulated to the mounted, 8-inch radius (17° DNA, double-helical slope) metal waxing template. The unmounted maxillary base plate and wax bite rim is finished to the marked, midline vestibular lip height. Both bite rims, the maxillary cast with only the wax bite rim and the mandibular occlusal rim with the full complement of teeth in wax, are returned to the clinician for modifications.
After the second clinical appointment, during which the modifications to the maxillary bite rim (of midline, of Cupid’s bow, of high lip-line, of incisal height, of centric) and to the mandibular wax-up (to incisal position, to emergence profile angle, to neutral zone placement, to shade selection approval) are made, the maxillary and the mandibular occlusal rims are returned to the laboratory to mount the maxillary cast and for functional and esthetic waxing. Unless instructed to finish the case, the laboratory forwards the waxed maxillary and mandibular arches to the clinician for the final patient/clinician adjustments.
Prior to mounting the mandibular model, it is recommended that the right/left condylar, right/left side-shift, and incisal table angulation settings on semi-adjustable articulators be set to zero degrees and all lateral articulator movements be eliminated. This allows the DNA-regulated mandibular occlusal plane height to be the only mounting variable. The incisal guide pin is set to the vertical height of the 8-inch waxing template/mandibular plane of occlusion and the case mounted to the articulator. The maxillary cast and the accompanying occlusal centric bite record are mounted to the DNA-regulated, mandibular plane of occlusion of the mounted mandibular cast. At the clinician’s discretion, protrusive and lateral bite records may be recorded at the wax try-in appointment and programmed into the articulator prior to the final wax-up.
In addition to the full maxillary and mandibular denture treatment, the stress axis/DNA protocols have proven useful in treatment planning complex anterior hyper-eruption cases, financially determined staged-treatment protocols, immediate denture cases (that, under certain circumstances, may be completed with no wax try-in appointment), TMD/equilibration assessment, second opinion cases, reassessment of existing treatments in progress, and implant-retained removable dental prostheses.
The author would like to acknowledge the following resources for the editorial, case history, and laboratory contributions: Dani Dental, Tempe, Ariz; Master Craft Dental Lab Corp, Loveland, Colo; R. Wurtzebach, DDS, Denver, Colo; C. Belting, DDS, Alamosa, Colo; J. Murray, DDS, Glenwood Springs, Colo; M. Gadeken, DDS, Grand Junction, Colo; R. Ford, BS, Grand Junction, Colo; J. Drazek, DDS, MS, Grand Junction, Colo; Larry Pierce, CDT, Grand Junction, Colo; Morgan Yost, DDS, Delta, Colo; and Richard Hurd, DDS, Grand Junction, Colo. To my instructors, mentors, and colleagues, a sincere thank you. Your ideas inculcate the substance of this article.
Disclosure: Dr. Ford reports no disclosures.
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